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ICL3207E Datasheet(PDF) 6 Page - Intersil Corporation

Part No. ICL3207E
Description  /- 15kV ESD Protected, 3V to 5.5V, Low Power, 250kbps, RS-232 Transmitters/Receivers
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Maker  INTERSIL [Intersil Corporation]
Homepage  http://www.intersil.com/cda/home
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ICL3207E Datasheet(HTML) 6 Page - Intersil Corporation

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6
Receivers
The ICL32X7E each contain inverting receivers that convert
RS-232 signals to CMOS output levels and accept inputs up
to
±25V while presenting the required 3kΩ to 7kΩ input
impedance (see Figure 1) even if the power is off
(VCC = 0V). The receivers’ Schmitt trigger input stage uses
hysteresis to increase noise immunity and decrease errors
due to slow input signal transitions.
Receivers on the ICL3207E are always active. The
ICL3217E receivers disable when in the automatic
powerdown state, thereby eliminating the possible current
path through a shutdown peripheral’s input protection diode
(see Figures 2 and 3).
Low Power Operation
These 3V devices require a nominal supply current of
0.3mA, even at VCC = 5.5V, during normal operation (not in
powerdown mode). This is considerably less than the 11mA
current required by comparable 5V RS-232 devices,
allowing users to reduce system power simply by replacing
the old style device with the ICL3207E.
Low Power, Pin Compatible Replacement
Pin compatibility with existing 5V products (e.g., MAX207E),
coupled with the wide operating supply range, make the
ICL32X7E potential lower power, higher performance drop-
in replacements for existing ‘2X7E 5V applications. As long
as the
±5V RS-232 output swings are acceptable, the
ICL32X7E devices should work in most 5V applications.
When replacing a ‘207E or ‘237E device in an existing 5V
application, it is acceptable to terminate C3 to VCC as shown
on the Typical Operating Circuit. Nevertheless, terminate C3
to GND if possible, as slightly better performance results
from this configuration.
Automatic Powerdown (ICL3217E Only)
Even greater power savings is available by using the
ICL3217E which features an automatic powerdown function.
When no valid RS-232 voltages (see Figure 4) are sensed
on any receiver input for 30
µs, the ICL3217E automatically
enters its powerdown state (see Figure 5). In powerdown,
supply current drops to 1
µA, because the on-chip charge
pump turns off (V+ collapses to VCC, V- collapses to GND),
and the receiver and transmitter outputs three-state (see
Table 2). This micro-power mode makes the ICL3217E ideal
for battery powered and portable applications. Invalid
receiver levels occur whenever the driving peripheral’s
outputs are shut off (powered down) or when the RS-232
interface cable is disconnected. The ICL3217E powers back
up whenever it detects a valid RS-232 voltage level on any
receiver input (such as when the RS-232 cable is
reconnected). The time to recover from automatic
powerdown mode is typically 100
µs.
RXOUT
GND
≤ VROUT ≤ VCC
5k
RXIN
-25V
≤ VRIN ≤ +25V
GND
VCC
FIGURE 1. INVERTING RECEIVER CONNECTIONS
FIGURE 2. POWER DRAIN THROUGH POWERED DOWN
PERIPHERAL
OLD
VCC
POWERED
GND
VCC
Rx
Tx
VCC
CURRENT
FLOW
VOUT = VCC
RS-232 CHIP
DOWN
UART
SHDN = GND
TABLE 2. ICL3217E AUTOMATIC POWERDOWN OPERATION
RS-232 SIGNAL
PRESENT AT
RECEIVER
INPUT?
TRANSMITTER
OUTPUTS
RECEIVER
OUTPUTS
MODE
OF
OPERATION
YES
Active
Active
Normal
Operation
NO
High-Z
High-Z
Powerdown
Due to Auto
Powerdown
Logic
FIGURE 3. DISABLED RECEIVERS PREVENT POWER DRAIN
ICL3217E
TRANSITION
DETECTOR
RX
TX
VCC
VCC
TO
VOUT = HI-Z*
WAKE-UP
LOGIC
POWERED
DOWN
UART
V-
* IN AUTOMATIC
POWERDOWN
ICL3207E, ICL3217E


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